Isolation of the South China Sea from the North Pacific Subtropical Gyre since the latest Miocene due to formation of the Luzon Strait

Abstract

The North Pacific subtropical gyre (NPSG) plays a major role in present global ocean circulation. At times, the gyre has coursed through the South China Sea, but its role in the evolutionary development of that Sea remains uncertain. This work systematically describes a major shift in NPSG paleo-circulation evident from sedimentary features observed in seismic and bathymetric data. These data outline two contourite depositional systems—a buried one formed in the late Miocene, and a latest Miocene to present-day system. The two are divided by a prominent regional discontinuity that represents a major shift in paleo-circulation during the latest Miocene (~ 6.5 Ma). The shift coincides with the further restriction of the South China Sea with respect to the North Pacific due to the formation of the Luzon Strait as a consequence of further northwest movement of the Philippine Sea plate. Before that restriction, data indicate vigorous NPSG circulation in the South China Sea. Semi-closure, however, established a new oceanographic circulation regime in the latest Miocene. This work demonstrates the significant role of recent plate tectonics, gateway development, and marginal seas in the establishment of modern global ocean circulation.

Incision of Submarine Channels Over Pockmark Trains in the South China Sea

“…Alongslope channels such as A–A′ and F–F′ run parallel to the slope contours, whereas across‐slope channels (D–D′ and G–G′) developed perpendicularly to the slope topography (Figure 2). Previous studies interpreted the channels in the study area as moats and furrows formed by contour currents (Yin et al., 2021). However, some of the furrows and channels described in Yin et al.…”

“…The slope to the east of the GH does not present any across‐slope channels, probably because it is relatively gentle (<0.3°) and, therefore, relatively stable and less likely to be affected by gravity flows (Figures 2 and 4). In addition, it is known that bathymetric obstacles influence the dynamics of bottom currents and control the formation of alongslope channels (Hernández‐Molina et al., 2006; Yin et al., 2021). Thus, alongslope channels were preferentially formed around the GH and ZCP (Figure 2).…”

“…The South China Sea is a semi‐enclosed marginal sea connected to the Pacific Ocean through the Luzon Strait (Liu et al., 2008). At present, the western South China Sea comprises four main water masses: surface water (at a water depth between 0 and 750 m), intermediate water (at water depths between 750 and 1500 m), deep and bottom waters below 1,500 m (Quan & Xue, 2018; Yin et al., 2021). Quan and Xue (2018) proposed a layered circulation model for the western South China Sea in which current direction between 700 and 1500 m water depth is to the south in the northern part of the study area, but changes to a northward direction in the southern part (Figure 1a).…”

“…They are likely formed by alongslope currents. Alongslope channels identified near the foot of the GH and ZCP (e.g., F-F′ and A-A′; Figure 2b) are contourite moats and furrows associated with an isolated mounded drift recognized by Yin et al (2021) (Figure 3a). They are thus related to contour currents flowing along the GH and ZCP, which were strong enough to erode the seafloor and generate erosional truncations on the banks of alongslope channels (Figures 2a and S4 and S6 in Supporting Information S1).…”

Progressive Intensification of Pacific Deep Water Circulation Since the Early Pliocene

“…However, the cooling climate, especially since the Pleistocene, may induce more AABW production by brine rejection due to increased sea ice, and facilitate PDW to reach a more vigorous threshold at some particular times, proposed here at 2.15 and 0.96 Ma (Figure 3). Plate tectonics is indirectly controlling the long-term global ocean circulation at million-year timescales, through opening/closing, or deepening/shallowing of oceanic gateways, arcs, ridges, basins, and other tectonic features (Knutz, 2008;Paxman et al, 2019;Sauermilch et al, 2021;Straume et al, 2020;Yin et al, 2021). The Pacific plate and its coupled local plates have been moving northwest since at least the late Miocene (Hall, 2002;Müller et al, 2016;Wu et al, 2016).…”